High Molecular Weight (HMW)-kininogen was shown to form a 1:1 stoichiometric complex with either plasma prekallikrein or factor XI and the light chain of HMW-kininogen was shown to be responsible for this interaction. In this fashion HMW-kininogen functions as a plasma cofactor required for coagulation, fibrinolysis and kinin-formation. Activation of factor XI to factor XIa was shown to occur by limited proteolysis in which two 80,000 dalton disulfide-linked chains are each digested within interchain disulfide bonds to yield 50,000 and 30,000 dalton disulfide linked fragments. Factor XIa was shown to directly convert plasminogen to plasmin and appeared to be equipotent with kallikrein as a plasmenogen activator. Histamine was shown to recruit eosinophils into human skin however allergic individuals had a markedly heightened eosinophil response compared to non-atopics. A case of combined cold and cholinergic urticaria was successfully treated with atarax plus periactin and the time course of histamine release was contrasted for each type of challenge. Cyproheptadine was shown to inhibit the effects of histamine in vivo in cold urticaria but had no effect upon the release of histamine. Thus cold challenge of treated patients yielded brisk histamine release but no symptoms and cyproheptadine acts in vivo as a potent H-1 type histamine antagonist.